Methods and filter for isolating upstream ingress noise in a bi-directional cable system

Abstract

An upstream ingress filter (300) for isolating upstream ingress noise on a bi-directional cable system having an upstream band and a downstream band for carrying upstream signals and downstream signals, respectively. The upstream ingress filter (300) includes a DC switching element (310) for changing the DC voltage on the cable system at said cable access unit and a switchable notch filter (340) that switches ON and OFF in response to the DC switching element. The notch filter isolates upstream ingress noise by attenuating upstream signals in the upstream band when the upstream ingress filter is ON. Both the DC switching element (310) and the notch filter (340) are connected in parallel to the cable (301).

We claim: 
     
       1. A method for isolating upstream ingress noise on a bi-directional cable system comprising a cable control unit, a plurality of cables, and a plurality of cable access units, each one of said plurality of cables having an upstream band and a downstream band for carrying upstream signals and downstream signals, respectively, each one of said plurality of cable access units comprising an associated upstream ingress filter, each of said ingress filters comprising a DC switching element for changing a DC voltage on said one of said plurality of cables and a switchable notch filter responsive to said DC switching element for making an ingress noise measurement, said DC switching element and said switchable notch filter being in parallel to each other and said one of said plurality of cables said method comprising the steps of: activating at least one of said upstream ingress filters to prevent said upstream signals and any associated ingress noise from being transmitted from said one of said plurality of cable access units;   measuring said upstream ingress noise during said step of activating to determine a first upstream ingress level;   comparing said first upstream ingress level with a predetermined threshold level; and   determining whether or not one or more of said plurality of cable access units are responsible for introducing upstream ingress noise to said cable system in response to said step of comparing.   
     
     
       2. The method of claim 1 wherein said step of activating comprises activating one or more of said upstream ingress filters simultaneously. 
     
     
       3. The method of claim 1 wherein said step of activating comprises periodically activating at least one of said upstream ingress filters. 
     
     
       4. The method of claim 1 wherein said step of activating is performed remote from said cable control unit in response to commands from said cable control unit. 
     
     
       5. The method of claim 1 wherein said step of activating is performed locally in response to a switch on said one of said plurality of cable access units. 
     
     
       6. The method of claim 1, wherein said predetermined threshold level is determined from a previous ingress noise measurement having an ingress noise level of acceptable quality. 
     
     
       7. The method of claim 1, wherein said predetermined threshold level is determined from a previous ingress noise measurement having an ingress noise level of unacceptable quality. 
     
     
       8. A method for isolating upstream ingress noise on a bi-directional cable system comprising a cable control unit, a plurality of cables, and a plurality of cable access units, said cable system having an upstream band and a downstream band for carrying upstream signals and downstream signals, respectively, each one of said plurality of cable access units comprising an associated upstream ingress filter, each of said ingress filters comprising a DC switching element for changing a DC voltage on one of said plurality of said cables and a switchable notch filter responsive to said DC switching element, said method comprising the steps of: activating at least one of said upstream ingress filters to prevent said upstream signals and any associated ingress noise from being transmitted from said one of said plurality of cable access units associated with said at least one of said upstream ingress filters;   measuring said upstream ingress noise subsequent to said step of activating to determine a first upstream ingress level;   comparing said first upstream ingress level with a predetermined threshold level; and   determining whether or not one or more of said plurality of cable access units are responsible for introducing upstream ingress noise to said cable system in response to said step of comparing.